Multiple gear motor drive

1. A hydraulic drive comprising multiple gear motors each having a gear motor output shaft, and a common gear engaged by the output shafts of the multiple gear motors, wherein the multiple gear motors include respective meshed pairs of gears disposed in a common housing, one of the gears of each pair has an output shaft provided with a pinion gear for engaging the common gear, and the phase relationship between the pinion gear and corresponding gear of each gear set varies from gear set to gear set.

2. A hydraulic drive as set forth in claim 1 , wherein the common gear is a ring gear.

3. A hydraulic drive as set forth in claim 1 , wherein the common gear drives an output shaft of the hydraulic drive.

4. A hydraulic drive as set forth in claim 3 , wherein the multiple gear motors are housed within a housing, and the output shaft of the hydraulic drive extends from at least one end of the housing.

5. A hydraulic drive as set forth in claim 1 , wherein the gear motors are circumferentially equally spaced apart.

6. A hydraulic drive as set forth in claim 1 , comprising a controller for controlling operation of the gear motors to control output speed and torque of the hydraulic drive.

7. A vehicle comprising at least one drive wheel, and the hydraulic drive of claim 1 drivingly coupled to the drive wheel.

8. A hydraulic drive comprising multiple hydraulic motors each having an output shaft, and a common gear engaged by the output shafts of the multiple hydraulic motors, and wherein each hydraulic motor has a characteristic periodic torque ripple out of phase with the characteristic periodic torque ripple of at least one other hydraulic motor for cancelling torque ripple and thereby reducing the torque ripple at the common gear, wherein the hydraulic motors are gear motors.

9. A hydraulic drive as set forth in claim 8 , wherein the common gear drives an output shaft of the hydraulic drive.

10. A hydraulic drive as set forth in claim 9 , wherein the multiple hydraulic motors are housed within a housing, and the output shaft of the hydraulic drive extends from at least one end of the housing.

11. A hydraulic drive comprising multiple hydraulic motors each having an output shaft, and a common gear engaged by the output shafts of the multiple hydraulic motors, and wherein each hydraulic motor has a characteristic periodic torque ripple out of phase with the characteristic periodic torque ripple of at least one other hydraulic motor for cancelling torque ripple and thereby reducing the torque ripple at the common gear, wherein the multiple hydraulic motors are gear motors respectively including meshed pairs of gears disposed in a common housing.

12. A hydraulic drive as set forth in claim 11 , wherein one of the gears of each pair has an output shaft provided with a pinion gear for engaging the common gear.

13. A hydraulic drive comprising multiple hydraulic motors each having an output shaft, and a common gear engaged by the output shafts of the multiple hydraulic motors, and wherein each hydraulic motor has a characteristic periodic torque ripple out of phase with the characteristic periodic torque ripple of at least one other hydraulic motor for cancelling torque ripple and thereby reducing the torque le at the common gear, wherein each hydraulic motor has an output shaft provided with a pinion gear for engaging the common gear, and the phase relationship between the pinion gear and corresponding gear of each gear set varies from gear set to gear set.

14. A hydraulic drive as set forth in claim 13 , wherein the hydraulic motors are circumferentially equally spaced apart.

15. A hydraulic drive as set forth in claim 13 , comprising a controller for controlling operation of the hydraulic motors to control output speed and torque of the hydraulic drive.

16. A vehicle comprising at least one drive wheel, and the hydraulic drive of claim 13 drivingly coupled to the drive wheel.